1. Field of the Invention
This invention relates to electromagnetic radiation detection devices. More particularly, this invention relates to electromagnetic radiation detection devices which may be worn by an individual to alert such an individual of harmful levels of electromagnetic energy and which are useful over a broadband of frequencies.
2. Description of Prior Art
The use of high power radio and microwave frequencies in the military, commercial and consumer applications has grown substantially. The applications of high power electromagnetic sources are numerous, including for example, radars, satellite communication ground terminals, radio transmitting antennas and microwave ovens.
One problem with high power electromagnetic radiation is its potential harmful effects on a human body. The American National Standards Institute have established safety guidelines to prevent exposure to harmful levels of electromagnetic radiation.
Harmful levels of electromagnetic radiation may not be detected by an individual until permanent damage results. Accordingly, a work place in the vicinity of high power electromagnetic sources can be a dangerous environment. Therefore, there is a need for a device which can sense electromagnetic radiation and provide an alert signal indicating harmful ambient levels. Furthermore, because of the numerous applications of electromagnetic sources and the multitude of frequencies generated, such electromagnetic radiation detection devices having a broadband frequency performance are desirable.
Broadband electromagnetic radiation detection devices have been used in the art for many years. For example, U.S. Pat. No. 3,931,573 assigned to the assignee of the present invention, discloses a hand-held radiation detector. However, hand-held radiation detectors may sometimes be cumbersome and inconvenient. Therefore, radiation hazard meters which can be worn by an individual are both practical and desirable.
When constructing a personal radiation hazard meter, electromagnetic interference from a human body is a concern. It is known that interference in the form of electromagnetic scattering results when electromagnetic radiation reflects off a human body. Such scattered reflections interfere with the electromagnetic radiation being detected by the radiation detector.
To minimize body interference, the radiation sensors of personal radiation hazard meters require shielding of the electromagnetic radiation sensor from the user's body. The shield, however, may produce its own source of interference due to unwanted reflections.
The use of lossy material as a radiation absorber to absorb reflective radiation is well known in the art. However, even lossy material has a measurable reflective characteristic. Generally, the more highly absorbent the lossy material is the more reflective it is. This property of lossy material suggests that the use of multiple layers of lossy material having different absorbent (and, accordingly, reflective) characteristics would be most effective in eliminating reflective interference with the radiation sensors from the conductive shield.
In such case, less absorbent/reflective lossy material is disposed behind the radiation sensor, then at least a second layer of more absorbent/reflective lossy material is disposed behind the first layer and in front of the shield. An example of this technique is shown in U.S. Pat. No. 5,168,265 (Aslan).
Applicant discovered that a single uniform layer of lossy material provided superior results in eliminating reflective interference. Unlike the "backing" of "graduated" lossy material disclosed in U.S. Pat. No. 5,168,265, a uniform layer of lossy material disposed a selected spaced distance behind the sensor is used in conjunction with the radiation sensor of the meter of the present invention.